Australian impact structures >10 Km-large

The geological antiquity of Australian land surfaces and the sedimentary and volcanic cover of Precambrian cratons in the central and western parts of the continent, allow preservation of a range of circular features, including morphological and drainage rings, circular lakes, volcanic craters, tectonic domes, oval granite bodies, mafic igneous plugs, salt diapirs, and magnetic, gravity and seismic anomalies of unknown origin. These include 38 confirmed asteroid and meteorite impact structures and craters and more than 40 ring, dome and crater features of unknown origin. Many of these structures display structural and geophysical elements consistent with impacts. Exposed features include circular crater-like morphological patterns which may intersect pre-existing linear structural features, central morphological highs and unique thrust and fault patterns. Buried circular features include single or multi-ring magnetic patterns, circular magnetic quiet zones, corresponding gravity patterns and low velocity and non-reflective seismic zones. Discrimination between impact structures and igneous plugs, volcanic caldera and salt domes requires field work possibly drilling. Large circular structures such as Mount Ashmore and Gnargoo are considered to have convincing structural deformation features to warrant classification as likely impact structures. Examples of crater-form features containing elements consistent with, but unproven to be of, impact origin include Auvergne, Delamere, Fiery Creek, Monte Christo, Mount Moffatt, Tanami East, Youngerina, Tingha. Examples of buried multi-ring features of possible to probable impact origin include Augathella, Balfour Downs, Calvert Hills, Camooweal, Green Swamp Well, Herbert, Ikybon River, Ilkurka, Lennis, McLarty Hills, Mount Davies, Mulkara, Neale, Sheridan Creek, Oodjuongari and Renehan. The origin of the very large circular magnetic and gravity pattern of the Diamantina River drainage feature and the multiple TMI ring pattern of the Deniliquin-Booligal region remains unresolved. Compared with frequency distribution patterns of extra-terrestrial impact structures worldwide, the Australian record displays a relatively a common occurrence of large impact structures and relative depletion in small impact structures and craters, explained by the better preservation of large structures at deep crustal zones as compared to the erosion of small craters, and a good geophysical coverage of large parts of the continent.